Gamma Resonance Absorption (GRA) Transmission Imaging is an automatic-decision, non-invasive, non-destructive interrogation method. It detects explosives and distinguishes them from benign objects via spatial reconstruction of the nitrogen density distribution within the inspected item from several radiographic views. GRA is uniquely well-suited to inspection of large, massive items such as air-baggage aggregates, aviation and marine containers, heavy vehicles or railroad cars. One reason is that it combines excellent sensitivity and specificity to nitrogenous explosives with very high radiation penetration, the nitrogen-resonant gamma-ray probe being at 9.172 MeV. Moreover, GRA radiation doses to the environment and screened items are about one order-of-magnitude lower than with any X-ray-based interrogation method, and more than 2 orders of magnitude less than with fast-neutron-based methods.
GRA for explosives detection was first proposed by Soreq NRC to the Federal Aviation Administration (FAA) in 1985 and successfully taken by the inventors through several rounds of experimental feasibility. Notable among the latter are a proof-of-principle laboratory test on individual aviation baggage items (1989), a blind test on aviation baggage aggregates (1993) and a demo run on LD-3 aviation containers (1998). These tests were all conducted at existing accelerator facilities, since the resonant gamma-rays can only be produced with the required spectral quality by 1.746 MeV protons impinging on a 13C target.
In the initial stages (1986-93), the R&D on GRA was performed in collaboration with Los Alamos National Laboratory (LANL). The group there evolved a different philosophy to that of Soreq, with respect to: i) employing supplementary gamma-ray lines, ii) the detector of choice (non-resonant-response BGO (bismuth germanate) detectors, as opposed to Soreq's resonant-response nitrogen-rich liquid scintillators) as well as to iii) the inspection methodology (full, multi-view tomography, as opposed to Soreq's plurality of discrete radiographic views). These activities resulted in the following patents being granted to Soreq: IL-86826 (1988)/U.S. Pat. No. 4,941,162(1989)/Europe-89111291.4 (1989); IL-93188 (1990)/U.S. Pat. No. 5,125,015 (1991) and IL-94050 (1990)/U.S. Pat. No. 5,247,177 (1992).
Subsequently, the TRIUMF/Grumman group developed and patented their own version of a non-resonant detector (also employing BGO)—U.S. Pat. No. 5,282,235 (1993), GRA inspection-configuration and chlorine-detection expertise—U.S. Pat. No. 5,784,430 (1996), as well as accelerator target—U.S. Pat. No. 6,215,851 (1998).
Other patents on GRA have been granted to M.I.T, on simultaneous detection of nitrogen and oxygen—U.S. Pat. No. 5,251,240 (1990); Science Research Laboratory of Somerville, Mass., on body-nitrogen assaying—U.S. Pat. No. 5,273,044 (1991) and National Electrostatics Corp. of Middleton, Wis., on a GRA-dedicated accelerator concept—U.S. Pat. No. 5,631,526 (1995). Like the latter, the above-mentioned M.I.T patent also includes claims on beam-recycling.
Finally, several patents on Gamma-Resonance Scattering (GRS) applications, as opposed to GRA transmission-imaging, the topic of the present disclosure, have been granted to Scientific Innovations of Wainscott, N.Y.—U.S. Pat. No. 5,040,200 (1989), U.S. Pat. No. 5,293,414 (1991), U.S. Pat. No. 5,323,004 (1993) and to M.I.T—U.S. Pat. No. 5,115,459 (1990), U.S. Pat. No. 5,420,905 (1993). The latter also include claims on multi-element detection with bremsstrahlung beams. However, the basic properties and figures-of-merit of GRS-applications (particularly, with respect to its spatial imaging capability) differ so radically from those of GRA that the two techniques, although related in terms of their underlying physics, are not on a comparable footing at all.